1. Field of the Invention
The present invention relates to a capacitance-type dynamic-quantity sensor for detecting a dynamic physical quantity such as acceleration or angular velocity by detecting a change in capacitance, which accompanies any displacement of a structure manufactured by using a semiconductor process, and to a manufacturing method therefor.
2. Description of the Related Art
Up to now, there has been known an electrostatic capacitance-type dynamic-quantity sensor. As regards such a sensor, a weight displaced according to externally applied acceleration or angular velocity, and a beam for supporting the weight are formed inside a semiconductor substrate to detect a change in electrostatic capacitance between a movable electrode of the weight and a fixed electrode formed at a minute interval from the movable electrode. (refer to JP 08-094666 A, for example). FIG. 5 is a schematic diagram thereof. In this sensor, weights 51 and beams 52 are formed inside a semiconductor substrate 53 through microprocessing. Glass substrates (an upper substrate 54 and a lower substrate 55) are bonded together from both sides thereof to seal the weights 51 and the beams 52. For such bonding, generally adopted is anodic bonding or eutectic bonding with a high reliability from the viewpoint of air-tightness or vacuum sealing. On account of bonding at about 300 to 400° C., glass is used, which contains metal to such a degree that its thermal expansion coefficient matches with that of the semiconductor substrate lest thermal strain should occur after the whole is cooled down to the room temperature. Etching such glass containing a large amount of metal allows formation of minute spaces 56 and 57. Fixed electrodes 58 are obtained by forming metal films within the minute spaces 56 and 57 defined by etching.
However, with the method as disclosed in JP 08-094666A, because of a large number of metal ions in the glass substrate, which function to equalize the thermal expansion coefficients of the glass substrate and the semiconductor substrate to each other, etching for forming the minute spaces involves a great deal of surface roughness on inner walls thereof. As a result, an etching depth for each minute space is hardly controlled, leading to a variation in detection sensitivity due to a variation in distance between the electrodes. In addition, the fixed electrode laminated on the rough surface easily peels off or undergoes disconnection, resulting in a reduction in sensor reliability.